In the manufacturing field, several applications require the use of laser joining systems for joining elements together. Mostly, for metallic elements, the current method is to join them with a seam by welding or brazing. Laser welding or brazing, or even laser cladding, use the energy of a focused high power laser beam on a very small area to melt the edge of the joint or heat it.
Whichever joining technique is utilized, in many applications, overall dimensions, positions and tolerances of the parts to be welded are so precise that the joint can be joined without a seam tracking system. In others cases, welding a joint on an automated production line basis, for example, requires to automate the process, specially for car roof welding applications. In order to automate the process, a control and monitoring system is necessary to minimize the rejected parts due to defects associated with the erroneous position of the focal point of the high-power laser beam with respect to the workpiece and other variables. For example, one can use a tracking sensor to locate and follow the joint and then to positionally control the application of the laser heat source during relative motion of the joint and the welding system. In the case of laser joining, the tracking sensor must continuously resolve the joint location with high precision, as the laser beam impinging on the joint may be focused down to a diameter as small as 0.25 mm or less.
Contact tracking sensors have been used for this purpose but they are subjected to wear and other problems which generally lead to reliability issues. Therefore, non-contact tracking sensors have been preferred.
Non-contact tracking sensors based on the use of laser have thus been envisaged. For example, known in the art, there is a seam tracking laser welding tool proposed by Permanova Lasersystem AB which is described in an article from A. Lindskog entitled <<Seam Tracking Laser Welding Tool>>. As disclosed therein, a laser beam projects a tracking laser line at a suitable angle to the surface to be profiled. The reflected light from the laser line is observed along a line of sight normal to the surface and is conveyed to an optical sensor extending coaxially along the optical axis of the laser. The elevation of the observed linear surface can be determined by optical triangulation. From this can be obtained a precise profile of the observed linear surface in the field of view of the optical sensor, which lies in a viewing plane normal to the surface. The optical sensor response can then be processed to provide, in essence, a sectional view indicating surface profile.
It is well known in the art that resolving a joint of minute lateral dimensions and accurately tracking it while moving at acceptable speeds is a difficult task. Moreover, the tracking sensor must allow controlling the laser welding beam such that it is both vertically and laterally aligned with the joint. The previously described device, which uses conventional CCD optical sensors, performs conveniently this tracking task but can not provide fast speed and accuracy required by some applications. Furthermore, it is bulky and requires adjustments of the laser projectors.
Besides, once a joint has been made, it would be desirable to perform an inspection of the seam in order to ensure the joint has been correctly made. Therefore, it would be desirable to provide a tracking, joining and inspection system able to simultaneously perform the tracking, the joining and the inspection of the joint to be processed. It would also be even more desirable to provide such a system which would be able to perform adaptive process control such as process speed or laser power as non limitative examples.
In the art, there are provided tracking and inspection systems, but they are not able to deal with curvilinear joints while welding using high power laser without using cumbersome rotating devices that prevent the vision system to view close to the processing area. This situation causes two major constraints. Firstly, the necessary space of all required devices to execute all these tasks is too large for easy access to the part without creating mechanical interference or colliding with the tooling or work piece. Moreover, the distance between the process point and the inspection point is too large to enable high accuracy of measurement and quick control action.
Known in the art, there is also U.S. Pat. Nos. 6,614,002; 6,621,047 and 4,673,795 but none of them disclose a tracking, joining and inspection system able to simultaneously perform the tracking, the joining and the inspection of the joint while being fast and accurate.
It would therefore be desirable to provide a device that incorporates in a compact assembly all the necessary elements to perform the tracking, the joining and the inspection of the joint to be processed while providing a fast processing speed.